Method for producing unsaturated aldehyde and unsaturated carboxylic acid

ABSTRACT

Disclosed is a method of a gas-phase catalytic oxidation reaction of propylene, isobutylene, or tertiary butanol with molecular oxygen in the presence of a catalyst to produce a corresponding unsaturated aldehyde and a corresponding unsaturated carboxylic acid, in which the catalyst can be used over a long period of time. Concretely, in the presence of the catalyst containing a complex oxide including molybdenum, bismuth and iron as essential components, at least one factor of a reaction pressure and a molar ratio of molecular oxygen to a raw material is controlled to change in such a way that a rate of reaction of the raw material is kept constant in the temperature range of from (TA−15)° C. to TA° C., when a boundary temperature of the activation energy of the catalyst is set to be TA° C.

This application is a 371 of PCT/JP2007/054245, filed Mar. 6, 2007.

TECHNICAL FIELD

The present invention relates to a method for producing an unsaturatedaldehyde and an unsaturated carboxylic acid, to be more precise, to amethod for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid through gas-phase catalytic oxidation of propylene,isobutylene, or tertiary butanol with molecular oxygen in the presenceof a catalyst.

BACKGROUND ART

The method for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid through gas-phase catalytic oxidation of propylene,isobutylene, or tertiary butanol with molecular oxygen in the presenceof a catalyst has been widely known and also has been industrially used.As the catalyst, for example, the one containing a complex oxideincluding molybdenum, bismuth and iron as essential components is used(Patent Documents 1 to 6). In this case, the reaction is carried outusing the catalyst in a fixed-bed at a temperature of 300 to 400° C.

Such a catalyst which is used in a gas-phase catalytic oxidationreaction is used for a relatively long period of time, and usually,activity of the catalyst is lowered and hence a rate of reaction of araw material is lowered with time. Usually, in a fixed-bed reactor,reaction temperature is raised to an allowable temperature of a processto maintain the rate of reaction of the raw material in response to theactivity-lowering with time (Patent Document 7 and Non-Patent Document1).

-   Patent Document 1: Japanese Patent Application Laid-Open No. Sho    53-19,188-   Patent Document 2: Japanese Patent Application Laid-Open No. Sho    54-66,610-   Patent Document 3: Japanese Patent Application Laid-Open No. Sho    55-359-   Patent Document 4: Japanese Patent Application Laid-Open No. Sho    55-19,227-   Patent Document 5: Japanese Patent Application Laid-Open No. Sho    56-95,135-   Patent Document 6: Japanese Patent Application Laid-Open No. Sho    60-28,824-   Patent Document 7: Japanese Patent Application Laid-Open No. Hei    11-263,739-   Non-Patent Document 1: Yuichi Murakami ed., “Mechanism of Catalyst    Degradation and Prevention Method”, p. 17, Technical Information    Institute Co., Ltd.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, through the investigation of the present inventors, it ispresumed that such controls of temperature only as those described inPatent Document 7 and Non-Patent Document 1 cannot always besufficiently satisfactory from the viewpoint of industrial practicebecause speed of activity lowering is relatively fast.

Consequently, it is an object of the present invention to provide amethod for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid, corresponding to polyprolylene, isobutylene, ortertiary butanol, through gas-phase catalytic oxidation of theaforementioned propylene, isobutylene, or tertiary butanol withmolecular oxygen in the presence of a catalyst, in which the catalystcan be used for a long period of time.

Means for Solving the Problem

The present invention is a method for producing an unsaturated aldehydeand an unsaturated carboxylic acid through gas-phase catalytic oxidationof propylene, isobutylene or tertiary butanol, which is a raw material,with molecular oxygen in the presence of a catalyst comprising a complexoxide including molybdenum, bismuth and iron as essential components,the method comprising:

controlling to change a reaction pressure in such a way that a rate ofreaction of the raw material is kept constant in the temperature rangeof from (TA−15)° C. to TA° C., when a boundary temperature of theactivation energy of the catalyst is set to be TA° C.

Further, the present invention is a method for producing an unsaturatedaldehyde and an unsaturated carboxylic acid through gas-phase catalyticoxidation of isobutylene or tertiary butanol, which is a raw material,with molecular oxygen in the presence of a catalyst comprising a complexoxide including molybdenum, bismuth and iron as essential components,the method comprising:

controlling to change a molar ratio of oxygen to the raw material insuch a way that a rate of reaction of the raw material is kept constantin the temperature range of from (TA−15)° C. to TA° C., when a boundarytemperature of the activation energy of the catalyst is set to be TA° C.The method can further comprise controlling to change a reactionpressure.

Effect of the Invention

According to the method for producing an unsaturated aldehyde and anunsaturated carboxylic acid of the present invention, catalyst can bepractically used over a long period of time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: A diagram showing a control method of the second reaction inExample 1

FIG. 2: A diagram showing a control method of the second reaction inExample 2

FIG. 3: A diagram showing a control method of the second reaction inExample 3

FIG. 4: A diagram showing a control method of the second reaction inExample 4

FIG. 5: A diagram showing a control method of the second reaction inComparative Example 1

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a catalyst containing a complex oxideincluding molybdenum, bismuth and iron as essential components is usedwhen propylene, isobutylene or tertiary butanol (hereinafter, expressedalso as “TBA”) is catalytically oxidized in a gas-phase with molecularoxygen to produce a corresponding unsaturated aldehyde and acorresponding unsaturated carboxylic acid. When propylene is the rawmaterial, the corresponding unsaturated aldehyde and unsaturatedcarboxylic acid are acrolein and acrylic acid, respectively, and whenisobutylene or tertiary butanol is the raw material, the correspondingunsaturated aldehyde and unsaturated carboxylic acid are methacroleinand methacrylic acid, respectively.

The catalyst to be used in the present invention is composed of acomplex oxide including molybdenum, bismuth and iron as essentialcomponents, and there is no limitation for components other than theessential components in the complex oxide in particular. Such a catalystcan be obtained by publicly known methods such as those described inPatent Documents 1 to 6.

The catalyst to be used in the present invention is preferably thecomplex oxide that has the composition represented by the followingformula (1).Mo_(a)Bi_(b)Fe_(c)M_(d)X_(e)Y_(f)Z_(g)Si_(h)O_(i)  (1)

In the formula (1), Mo, Bi, Fe, Si, and O represent molybdenum, bismuth,iron, silicone, and oxygen, respectively. M represents at least oneelement selected from the group consisting of cobalt and nickel. Xrepresents at least one element selected from the group consisting ofchromium, lead, manganese, calcium, magnesium, niobium, silver, barium,tin, tantalum and zinc. Y represents at least one element selected fromthe group consisting of phosphorus, boron, sulfur, selenium, tellurium,cerium, tungsten, antimony, and titanium. Z represents at least oneelement selected from the group consisting of lithium, sodium,potassium, rubidium, cesium, and thallium. Each of a, b, c, d, e, f, g,h, and i represents an atomic ratio of each element, respectively, andwhen a is 12, b is from 0.01 to 3, c is from 0.01 to 5, d is from 1 to12, e is from 0 to 8, f is from 0 to 5, g is from 0.001 to 2, h is from0 to 20, and i is the atomic ratio of oxygen that fulfills therequirement of the valence of each component mentioned above.

The complex oxide that is the catalyst to be used in the presentinvention may be supported on a carrier. As the carrier, silica,alumina, silica-alumina, magnesia, titania, silicon carbide, or the likecan be listed.

Hereinafter, a preferable method of production of the catalyst to beused in the present invention will be explained.

As the raw materials of the elements that constitute the catalyst(hereinafter, sometimes abbreviated to “raw materials for catalyst”),though they are not particularly limited, ordinarily, oxides, chlorides,hydroxides, sulfates, nitrates, carbonates, acetates, ammonium salts, ormixtures of these materials can be used. In the case of using chlorides,it is preferable to select candidates from chlorides that can be changedto oxides when ignited. Further, it is possible to use, in particular,metals and sparingly soluble compounds in addition to commonly usedwater soluble compounds

First, a solution or a dispersion liquid (liquid A) that contains atleast molybdenum is prepared. In other words, at least a raw material ofmolybdenum is dissolved or dispersed in a solvent. As the raw materialof molybdenum, it is preferable to use ammonium paramolybdate, however,various raw materials such as molybdenum trioxide and molybdenumchloride can also be used. Further, a part or the whole of the rawmaterials for catalyst corresponding to bismuth, M component, Xcomponent, Y component, Z component, and silicon in the case ofproducing the catalyst represented by the aforementioned formula (1) canbe added to the liquid A, in the course of preparing the liquid A orafter preparing the liquid A. However, it is preferable not to add a rawmaterial of iron, and hence, it is preferable that the liquid A do notcontain iron.

As the solvent of the liquid A, water, alcohol, acetone, or the like canbe used. A mixed solvent of two or more kinds of these solvents is alsoavailable. It is preferable to use at least water as the solvent, and itis preferable that 50% by mass or more of the whole solvent be water.Further, it is also preferable to use water alone as the solvent.

The mass of the solvent to be used at the time of preparing the liquid Ais preferably 70 to 270 parts by mass with respect to 100 parts by massof the sum of the raw materials for catalyst to be added to the liquidA.

On the other hand, a solution or a dispersion liquid (liquid B) thatcontains at least iron is prepared. In other words, at least a rawmaterial of iron is dissolved or dispersed in a solvent. As the rawmaterial of iron, ferric nitrate is preferable, however, various rawmaterials such as iron hydroxide and iron trioxide can also be used.Further, a part or the whole of the raw materials for catalystcorresponding to bismuth, M component, X component, Y component, Zcomponent, and silicon in the case of producing the catalyst representedby the aforementioned formula (1) can be added to the liquid B, in thecourse of preparing the liquid B or also after preparing the liquid B.However, it is preferable not to add a raw material of molybdenum, andhence, it is preferable that the liquid B do not contain molybdenum.

As the solvent of the liquid B, water, alcohol, acetone, or the like canbe used. A mixed solvent of two or more kinds of these solvents is alsoavailable. It is preferable to use at least water as the solvent, and itis preferable that 50% by mass or more of the whole solvent be water.Further, it is also preferable to use water alone as the solvent.

The mass of the solvent to be used at the time of preparing the liquid Bis preferably to 230 parts by mass with respect to 100 parts by mass ofthe sum of the raw materials for catalyst to be added to the liquid B.

Subsequently, a solution or a dispersion liquid (liquid C) is preparedby mixing the liquid A and liquid B prepared as mentioned above.Further, a part or the whole of the raw materials for catalystcorresponding to bismuth, M component, X component, Y component, Zcomponent, and silicon in the case of producing the catalyst representedby the aforementioned formula (1) can be added to the liquid C, in thecourse of preparing the liquid C or also after preparing the liquid C.And thus, liquid D is finally prepared.

The raw materials of bismuth, M component, X component, Y component, Zcomponent, and silicon may be added in such a way that necessary amountsof respective elements are contained in the liquid D finally obtained.Therefore, each raw material for catalyst may be added to any one of theliquid A, liquid B, and liquid C at a time, or may be divided into twoor more and added separately to at least one of the liquid A, liquid B,and liquid C at a plurality of times.

The solution or dispersion liquid (liquid D) that contains at leastmolybdenum, bismuth and iron can be prepared by the methods mentionedabove using the necessary raw materials for catalyst. In the case ofproducing a catalyst in which a complex oxide is supported on a carrier,the carrier may be caused to coexist in the liquid D and the followingtreatment may be carried out.

Subsequently, it is preferable to hold the obtained liquid D at atemperature in the range of from 80 to 120° C. The holding temperatureis more preferably in the temperature range of from 90 to 120° C. Whenthe temperature of the liquid D is held in this temperature range,catalyst performance can be further improved.

The holding time is not particularly limited, however, it is suitably inthe range of from 1 second to 30 hours, preferably in the range of from1 minute to 30 hours, and particularly preferably in the range of from 3minutes to 15 hours. When the holding time is too short, the effect ofimproving catalyst performance by holding can hardly be obtained.Further, when the holding time is too long, any additional effect by theprolonged holding can hardly be obtained. The reason for the furtherimprovement of the catalyst performance by the holding is not clear,however, it is presumed that reactivity of the catalyst precursor isimproved, so that the catalyst performance is improved.

Subsequently, drying and calcination are carried out when necessary. Asthe method of drying, various drying methods such as a box type dryer,evaporative drying, and spray drying can be used. The drying conditionis preferably 30 to 150° C. in the case of the box type dryer and 100 to500° C. as an inlet temperature in the case of a spray dryer. Further,as the calcining condition, though it is not particularly limited, apublicly known condition can be adopted. The calcination is usuallycarried out in the temperature range of from 200 to 600° C. and over theperiod of from 0.5 to 10 hours. It is preferable to carry out thecalcination separately, namely, decomposition of salts and a subsequentcalcination.

Subsequently, the obtained catalyst can be molded. The method formolding the catalyst is not particularly limited, and the catalyst canbe molded in an optional shape such as spherical shape, ring shape,cylindrical shape, or star shape using a molding machine for generalpowder such as tablet machine, extruder, or rolling pelletizer.

Further, conventionally known additives, for example, like organiccompounds such as polyvinyl alcohol and carboxymethylcellulose may befurther added. Further, inorganic compounds such as graphite anddiatomaceous earth and inorganic fibers such as glass fiber, ceramicfiber, and carbon fiber may also be added.

The molded catalyst is subjected to heat treatment when necessary. Thecondition of the heat treatment is not particularly limited, and apublicly known condition for heat treatment can be applied. The heattreatment is usually carried out in the temperature range of from 150 to600° C. for 0.5 to 80 hours.

As mentioned above, the catalyst composed of a complex oxide includingat least molybdenum, bismuth and iron can be obtained.

The catalyst can be used while diluted with an inert substance such assilica, alumina, silica-alumina, magnesia, titania, or silicon carbide.

In the present invention, propylene, isobutylene or tertiary butanol,which is a raw material, is catalytically oxidized in a gas-phase withmolecular oxygen in the presence of the aforementioned catalyst toproduce a corresponding unsaturated aldehyde and unsaturated carboxylicacid. For example, the gas-phase catalytic oxidation can be carried outby passing a feed gas containing the raw material and molecular oxygenthrough a reactor packed with the aforementioned catalyst.

As a source of the molecular oxygen, air is economical, however, pureoxygen-enriched air can be used when necessary. The concentration ratio(molar ratio) of the molecular oxygen to the raw material in the feedgas is preferably in the range of from 0.5/1 to 3/1. It is preferablethat an inert gas be contained in the feed gas for dilution. The feedgas may contain water vapor. The concentration of the raw material inthe feed gas is preferably 1 to 10% by volume.

The reaction pressure is preferably 20 to 300 kPa (gauge pressure;hereinafter, pressure being expressed in gauge pressure) as an averageof inlet pressure and outlet pressure of the reaction tube. The reactiontemperature can be selected in the range of from 200 to 450° C. Thereaction temperature is preferably in the range of from 250 to 400° C.and more preferably in the range of from 310 to 380° C.

However, the activity of such a catalyst that is used in a gas-phasecatalytic oxidation declines with time. As the cause of the declinationof the activity, there are various theories such as decomposition ofcatalyst structure by temperature (sublimation or vaporization ofcatalyst components; change in crystalline phase in catalyst structure),reduction of catalyst components by reactants, and reduction of catalystcomponents by reactants and temperature. The present inventors havediligently examined these issues and found that the decomposition ofcatalyst structure by temperature or the reduction of catalystcomponents by reactants and temperature is the dominative cause of thedeterioration of the activity in the present catalyst system, and theyhave completed the present invention.

Namely, in the present invention, at least one factor of reactionpressure and molar ratio of the molecular oxygen to the raw material(O/R) in the feed gas is controlled to change within the temperaturerange of from (TA−15)° C. to TA° C. (here, TA (° C.) being a boundarytemperature of the activation energy of the catalyst) so as to maintainthe rate of reaction of the raw material without raising the reactiontemperature as far as possible. By carrying out such a control, thethermal decomposition of catalyst structure or the reduction of catalystcomponents by reactants and temperature change can be suppressed, andthe time of use of the catalyst (catalyst life) is rapidly improved incomparison with the conventional case where only the reactiontemperature is controlled. The TA (° C.) can be obtained by the methoddescribed in Patent Document 7.

It is known in a gas-phase catalytic reaction using a solid catalystthat the activation energy of the reaction in question often showsdifferent values in each of a low reaction temperature range and highreaction temperature range with a certain reaction temperature being aboundary. For example, it is reported in Journal of Catalysis, Vol. 41,pp 134-139 that such different activation energies as those mentionedabove are observed in the catalytic oxidation reaction of 1-butane on acatalyst composed of a composite oxide including molybdenum and bismuth.The reason why such a phenomenon is observed is because therate-determining step is different depending on the reactiontemperature, which is described in detail in Shokubai Koza (CatalysisCourse), Vol. 1, Chap. 4, Kodansha Ltd. (edited by Catalysis Society ofJapan). According to another opinion, it is presumed that a reaction ofreactant molecules on the catalyst active center be the rate-determiningstep in the low reaction temperature range while diffusion of reactantmolecules to the catalyst active center be the rate-determining step inthe high reaction temperature range.

The present inventors have analyzed the activation energy of thereaction that produces methacrolein and methacrylic acid throughgas-phase catalytic oxidation of isobutylene with molecular oxygen inthe presence of a catalyst composed of a complex oxide includingmolybdenum, bismuth and iron as essential components, and they haveconfirmed that the activation energy shows different values in each of alow reaction temperature range and high reaction temperature range.

In the present invention, the boundary temperature of the activationenergy TA (° C.) can be obtained as follows. First, a catalyst is packedin a reaction tube equipped with Thermo-bath, and the temperature of theThermo-bath is changed in the range of 315 to 375° C. at an interval of2 to 5° C., and a rate of reaction of isobutylene is obtained at eachtemperature. Here, the rate of reaction of isobutylene is obtained bythe following equation.Rate of reaction of isobutylene (%)=A/B×100(A represents number of moles of isobutylene reacted and B representsnumber of moles of isobutylene supplied.)K=(SV)×(1/ρ)×ln [100/(100−X)](K represents reaction rate constant, SV represents space velocity, ρrepresents packing density of a catalyst, and X represents rate ofreaction (%) of a raw material, respectively.)

Subsequently, 1/T is plotted as horizontal axis and ln K is plotted asvertical axis, and after each datum was plotted, two linearapproximation lines were drawn and inclinations of these lines wereobtained. Here, 1/T represents the reciprocal of a Thermo-bathtemperature (absolute temperature) of the reaction tube and ln Krepresents a natural logarithm of the reaction rate constant. The linearapproximation line can be obtained by a general method such as the leastsquares method. The absolute value of the inclination of the obtainedlinear approximation line multiplied by gas constant equals theactivation energy to be obtained, and the reciprocal of the value on thehorizontal axis of the intersection of the two linear approximationlines is the boundary temperature of the activation energy TA (° C.) tobe obtained.

In the case that tertiary butanol is used as the raw material instead ofisobutylene, tertiary butanol is immediately decomposed to isobutyleneand water in the presence of the catalyst containing molybdenum, bismuthand iron as essential components. In other words, when tertiary butanolis used as the raw material, a reaction scheme is also thought to beessentially same as the oxidation reaction of isobutylene. Therefore, inthe case that tertiary butanol is used as the raw material, the sameboundary temperature of the activation energy of the reaction ofisobutylene can also be used.

In the case that propylene is used as the raw material, the boundarytemperature of the activation energy can also be obtained in the sameway as in the case of isobutylene.

It is effective to control the reaction pressure so as to rise with theprogress of the reaction. The reaction pressure at the start of thereaction is preferably 90 to 110 kPa and more preferably 95 to 105 kPa.The reaction pressure at the end of the reaction is preferably 105 to125 kPa and more preferably 110 to 120 kPa. The reaction pressure may beraised continuously, however, it is preferably raised stepwise from theviewpoint of easiness of control. When the reaction pressure is raisedstepwise, it is preferably raised in two steps or more. When thereaction pressure is raised in two steps, for example, it is preferableto set the first reaction pressure at 95 to 105 kPa, to once set thereaction pressure at 100 to 110 kPa in the middle of the reaction, andto finally set the reaction pressure at 110 to 120 kPa. Here, thereaction pressure means the average of inlet pressure and outletpressure of the reactor.

It is effective to control the molar ratio of the molecular oxygen tothe raw material (O/R) in the feed gas so as to rise with the progressof the reaction. The molar ratio (O/R) at the start of the reaction ispreferably 1.8 to 2.2 and more preferably 1.9 to 2.1. The molar ratio(O/R) at the end of the reaction is preferably 2.1 to 2.5 and morepreferably 2.2 to 2.4. The molar ratio (O/R) may be raised continuously,however, it is preferably raised stepwise from the viewpoint of easinessof control. When the molar ratio (Q/R) is raised stepwise, it ispreferably raised in two steps or more. When the molar ratio (O/R) israised in two steps, for example, it is preferable to set the firstmolar ratio (O/R) at 1.95 to 2.05, to once set the molar ratio (O/R) at2.10 to 2.20 in the middle of the reaction, and to finally set the molarratio (O/R) at 2.25 to 2.35.

Either the reaction pressure or the molar ratio of the molecular oxygento the raw material (O/R) in the feed gas may be controlled to change,however, a large effect can be obtained when both the reaction pressureand the molar ratio are controlled to change. When both of them arechanged, they may be changed simultaneously or alternately.

When at least one factor of the reaction pressure and the molar ratio ofthe molecular oxygen to the raw material in the feed gas is changed, thecondition may be restored with the elapse of time depending on theextent of the change in the catalyst activity.

The change in at least one factor of the reaction pressure and the molarratio of the molecular oxygen to the raw material in the feed gas iscarried out in such a way that the rate of reaction of the raw materialbecomes constant. Here, “the rate of reaction of the raw material isconstant” means the rate of reaction is within ±2% of the rate ofreaction of operation management at the time of normal operation. Therate of reaction of operation management is a target rate of reaction atthe time of normal operation. For example, a method in which at leastone factor of the reaction pressure and the molar ratio of the molecularoxygen to the raw material in the feed gas is changed, when the rate ofreaction of the raw material is lowered to (the rate of reaction of theraw material at the start of the reaction−2%), so as to cause the rateof reaction of the raw material not to exceed (the rate of reaction ofthe raw material at the start of the reaction+2%) is available.

As mentioned above, TBA is immediately decomposed to isobutylene andwater in the presence of the catalyst containing molybdenum, bismuth andiron as essential components. Therefore, the rate of reaction of TBA iscalculated regarding isobutylene as the raw material based on theassumption that 100% of TBA is decomposed to isobutylene.

A higher effect can be obtained by controlling to change the reactiontemperature in addition to controlling to change at least one factor ofthe reaction pressure and the molar ratio of the molecular oxygen to theraw material (O/R) in the feed gas.

The production method of the present invention can be used incombination with the activation treatment such as one described inPatent Document 7. Namely, it is possible to carry out activation byholding the catalyst under the temperature in the range of 300° C. orabove to less than 550° C. and bringing the catalyst into contact withthe gas practically composed of air for 1 hour or more.

The catalyst used in the reaction under the above-mentioned control canalso be used further in an ordinary gas-phase catalytic oxidation, andin that case, the time of use of the catalyst (catalyst life) isimproved.

EXAMPLES

Hereinafter, the present invention will be explained by examples. In theexplanation, “part” means part by mass. The analyses of the reactionproducts were carried out with gas chromatography. Further, rate ofreaction of isobutylene as the raw material and selectivities tomethacrolein and methacrylic acid to be produced are defined as follows.Rate of reaction of the raw material (%)=A/B×100(A represents number of moles of the raw material reacted and Brepresents number of moles of the raw material supplied.)Selectivity to methacrolein (%)=C/A×100(A represents number of moles of the raw material reacted and Crepresents number of moles of methacrolein produced.)Selectivity to methacrylic acid (%)=D/A×100(A represents number of moles of the raw material reacted and Drepresents number of moles of methacrylic acid produced.)

The composition of the catalyst precursor powder other than oxygen wasestimated with ICP Atomic Emission Spectrometry and atomic absorptionspectrometry of the catalyst precursor powder dissolved in hydrochloricacid.

Reference Example Catalyst Preparation

To 6,000 parts of water, 3,000 parts of ammonium paramolybdate weredissolved, and then 330.2 parts of antimony trioxide were added whilethe resultant mixture was stirred, and the resultant mixture was heatedto 50° C. to obtain liquid A. Separately, to 5,500 parts of water, 972.5parts of iron nitrate (III), 3,296.8 parts of cobalt nitrate, 84.3 partsof zinc nitrate, and 110.4 parts of cesium nitrate were dissolved, andto the resultant mixture, a solution obtained by dissolving 150 parts of60% by mass nitric acid aqueous solution and 480.8 parts of bismuthnitrate in 300 parts of water was added, and the resultant mixture washeated to 30° C. to obtain liquid B.

The liquid B was added to the liquid A while the resultant mixture wasstirred to obtain a slurry substance, and the slurry substance was agedat 90° C. for 2 hours, and heated to 103° C. and concentrated for 1hour, and spray dried to obtain dry powder. The obtained dry powder wascalcined at 300° C. for 4 hours to obtain a catalyst precursor powderhaving the following composition.Mo₁₂Bi_(0.7)Fe_(1.7)Co₈Zn_(0.2)Cs_(0.4)Sb_(0.8)O_(x)(In the above formula, MO, Bi, Fe, Co, Zn, Cs, Sb, and O representmolybdenum, bismuth, iron, cobalt, zinc, cesium, antimony, and oxygen,respectively. Further, the numeral written at the right side of eachchemical symbol represents an atomic ratio, and x represents the atomicratio of oxygen that fulfills the requirement of the valence of eachcomponent mentioned above.)

With 80 parts of methyl cellulose powder, 3,920 parts of the obtainedcatalyst precursor powder were mixed, and to the resultant mixture,1,490 parts of pure water were added, and the resultant mixture waskneaded and molded into ring shape having outer diameter of 5 mm, innerdiameter of 2 mm, and height of 5 mm, and the molded article wassubjected to heat treatment of 510° C. for 2 hours to obtain a catalyst.

(Determination of the Boundary Temperature of the Activation Energy TA(° C.) of a Catalyst)

To a stainless steel reaction tube which has inside diameter of 27.5 mmand height of 4 m and is equipped with Thermo-bath outside, 2,000 g ofthe obtained catalyst were packed. Subsequently, a gas-phase catalyticoxidation of isobutylene was carried out under the condition where afeed gas composed of 5% by volume of isobutylene, 12% by volume ofoxygen, 10% by volume of water vapor, and 73% by volume of nitrogen waspassed through the catalyst layer at a contact time of 3.5 seconds andthe temperature of the Thermo-bath was changed in the range of 315 to375° C. at an interval of 2 to 5° C., and an activation energy wascalculated from the rate of reaction of isobutylene at respectivetemperatures. As a result, the boundary temperature of the activationenergy TA (° C.) was 335° C., and the activation energy of the lowertemperature side of the boundary temperature was 100 kJ/mol, and that ofhigher temperature side was 32 kJ/mol. The average reaction pressure was98 kPa.

Example 1 The First Reaction

To the reaction tube used in the Reference Example, 2,000 g of thecatalyst obtained in the Reference Example was packed. Subsequently, thetemperature of the Thermo-bath was set to 320° C., and a gas-phasecatalytic oxidation of isobutylene was carried out under the conditionwhere a feed gas composed of 5% by volume of isobutylene (the rawmaterial of the reaction), 9% by volume of oxygen, 10% by volume ofwater vapor, and 76% by volume of nitrogen was passed through thecatalyst layer at a contact time of 4.5 seconds. As a result ofanalyzing the reaction products in an early stage, the rate of reactionof isobutylene was 95.7%, the selectivity to methacrolein was 87.9%, andthe selectivity to methacrylic acid was 5.4%. At this stage, thetemperature of the Thermo-bath was 320° C., the average reactionpressure was 100 kPa, and the molar ratio of the molecular oxygen to theraw material in the feed gas was 2.0 (initial reaction condition).

The Second Reaction

Following the first reaction, control was carried out with the rate ofreaction of operation management being 95%. Concretely, the temperatureof the Thermo-bath, the average reaction pressure, and the molar ratioof the molecular oxygen to the raw material in the feed gas were changedas shown in FIG. 1. The duration of continuous operation became 14,700hours. As a result of analyzing the reaction products at this stage, therate of reaction of isobutylene was 95.7%, the selectivity tomethacrolein was 87.8%, and the selectivity to methacrylic acid was5.3%. At this stage, the temperature of the Thermo-bath was 335° C., theaverage reaction pressure was 110 kPa, and the molar ratio of themolecular oxygen to the raw material in the feed gas was 2.3 (reactioncondition 1).

The Third Reaction

Following the second reaction, the reaction was once stopped, andresumed with the initial reaction condition. As a result of analyzingthe reaction products in an early stage of the resumed reaction, therate of reaction of isobutylene was 93.5%, the selectivity tomethacrolein was 87.7%, and the selectivity to methacrylic acid was5.3%.

The Fourth Reaction

Following the third reaction, the reaction condition was changed to thereaction condition 1, and the reaction was continued till thetemperature of the Thermo-bath became 360° C. while the temperature ofthe Thermo-bath was controlled to rise in such a way that the rate ofreaction of isobutylene became constant. The duration of continuousoperation became 19,200 hours in all. As a result of analyzing thereaction products at this stage, the rate of reaction of isobutylene was95.7%, the selectivity to methacrolein was 87.6%, and the selectivity tomethacrylic acid was 5.3%.

Example 2 The First Reaction

The first reaction was carried out in the same manner as in Example 1.

The Second Reaction

Following the first reaction, the second reaction was carried out in thesame manner as in Example 1 except that the temperature of theThermo-bath and the average reaction pressure were changed as shown inFIG. 2. The duration of continuous operation became 7,520 hours. As aresult of analyzing the reaction products at this stage, the rate ofreaction of isobutylene was 95.6%, the selectivity to methacrolein was87.9%, and the selectivity to methacrylic acid was 5.4%. At this stage,the temperature of the Thermo-bath was 335° C., the average reactionpressure was 110 kPa, and the molar ratio of the molecular oxygen to theraw material in the feed gas was 2.0 (reaction condition 2).

The Third Reaction

Following the second reaction, the third reaction was carried out in thesame manner as in Example 1. As a result of analyzing the reactionproducts in an early stage of the resumed reaction, the rate of reactionof isobutylene was 93.4%, the selectivity to methacrolein was 87.8%, andthe selectivity to methacrylic acid was 5.4%.

The Fourth Reaction

Following the third reaction, the fourth reaction was carried out in thesame manner as in Example 1 except that the reaction condition waschanged to the reaction condition 2, and the reaction was continued tillthe temperature of the Thermo-bath became 360° C. The duration ofcontinuous operation became 14,400 hours in all. As a result ofanalyzing the reaction products at this stage, the rate of reaction ofisobutylene was 95.6%, the selectivity to methacrolein was 87.7%, andthe selectivity to methacrylic acid was 5.4%.

Example 3 The First Reaction

The first reaction was carried out in the same manner as in Example 1.

The Second Reaction

Following the first reaction, the second reaction was carried out in thesame manner as in Example 1 except that the temperature of theThermo-bath and the molar ratio of the molecular oxygen to the rawmaterial in the feed gas were changed as shown in FIG. 3. The durationof continuous operation became 8,000 hours. As a result of analyzing thereaction products at this stage, the rate of reaction of isobutylene was95.7%, the selectivity to methacrolein was 87.9%, and the selectivity tomethacrylic acid was 5.4%. At this stage, the temperature of theThermo-bath was 335° C., the average reaction pressure was 100 kPa, andthe molar ratio of the molecular oxygen to the raw material in the feedgas was 2.3 (reaction condition 3).

The Third Reaction

Following the second reaction, the third reaction was carried out in thesame manner as in Example 1. As a result of analyzing the reactionproducts in an early stage of the resumed reaction, the rate of reactionof isobutylene was 93.5%, the selectivity to methacrolein was 87.9%, andthe selectivity to methacrylic acid was 5.4%.

The Fourth Reaction

Following the third reaction, the fourth reaction was carried out in thesame manner as in Example 1 except that the reaction condition waschanged to the reaction condition 3, and the reaction was continued tillthe temperature of the Thermo-bath became 360° C. The duration ofcontinuous operation became 15,000 hours in all. As a result ofanalyzing the reaction products at this stage, the rate of reaction ofisobutylene was 95.7%, the selectivity to methacrolein was 87.7%, andthe selectivity to methacrylic acid was 5.4%.

Example 4

The reaction was carried out in the same manner as in Example 1 exceptthat tertiary butanol (TBA) was used as the raw material instead ofisobutylene, and the temperature of the Thermo-bath, the averagereaction pressure, and the molar ratio of the molecular oxygen to theraw material in the feed gas were changed as shown in FIG. 4 in thesecond reaction. The rate of reaction of TBA is calculated regardingisobutylene as the raw material based on the assumption that 100% of TBAis decomposed to isobutylene.

As a result, the duration of continuous operation of the second reactionbecame 14,600 hours, and the duration of continuous operation throughthe fourth reaction became 19,100 hours.

Comparative Example 1 The First Reaction

The first reaction was carried out in the same manner as in Example 1.

Following the first reaction, the second reaction was carried out in thesame manner as in Example 1 except that the temperature of theThermo-bath was changed as shown in FIG. 5. The duration of continuousoperation became 4,600 hours. As a result of analyzing the reactionproducts at this stage, the rate of reaction of isobutylene was 95.4%,the selectivity to methacrolein was 88.0%, and the selectivity tomethacrylic acid was 5.5%. At this stage, the temperature of theThermo-bath was 335° C., the average reaction pressure was 100 kPa, andthe molar ratio of the molecular oxygen to the raw material in the feedgas was 2.0 (reaction condition 4).

TABLE 1 Control in the second reaction Duration of Duration of AverageMolar ratio of Temperature continuous continuous reaction Oxygen to ofoperation in the operation through Raw material pressure raw materialThermo-bath second reaction the fourth reaction Ex. 1 isobutylene ◯ ◯ ◯14,700 hours  19,200 hours Ex. 2 isobutylene ◯ ◯ 7,520 hours 14,400hours Ex. 3 isobutylene ◯ ◯ 8,000 hours 15,000 hours Ex. 4 TBA ◯ ◯ ◯14,600 hours  19,100 hours Comp. Ex. 1 isobutylene ◯ 4,600 hours —

1. A method for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid through gas-phase catalytic oxidation of propylene,isobutylene or tertiary butanol, which is a raw material, with molecularoxygen in the presence of a catalyst comprising a complex oxideincluding molybdenum, bismuth and iron as essential components, themethod comprising: controlling reaction pressure in such a way that arate of reaction of the raw material is kept constant in the temperaturerange of from (TA−15)° C. to TA° C., where TA° C. is the boundarytemperature of the activation energy of the catalyst, and controllingreaction pressure such that the reaction pressure rises with theprogress of the reaction of the raw material, wherein the reactionpressure at the start of the reaction is 90 to 110 kPa and is 105 to 125kPa at the end of the reaction, where reaction pressure is an average ofinlet pressure and outlet pressure and is expressed in gauge pressure.2. The method as claimed in claim 1, comprising controlling reactionpressure and the molar ratio of oxygen to the raw material in such a waythat a rate of reaction of the raw material is kept constant in thetemperature range of from (TA−15)° C. to TA° C.
 3. The method as claimedin claim 1, wherein said method is a method for producing an unsaturatedaldehyde and an unsaturated carboxylic acid through gas-phase catalyticoxidation of propylene with molecular oxygen.
 4. The method as claimedin claim 1, wherein said method is a method for producing an unsaturatedaldehyde and an unsaturated carboxylic acid through gas-phase catalyticoxidation of isobutylene with molecular oxygen.
 5. The method as claimedin claim 1, wherein said method is a method for producing an unsaturatedaldehyde and an unsaturated carboxylic acid through gas-phase catalyticoxidation of tertiary butanol with molecular oxygen.
 6. The method asclaimed in claim 2, wherein said method is a method for producing anunsaturated aldehyde and an unsaturated carboxylic acid throughgas-phase catalytic oxidation of propylene with molecular oxygen.
 7. Themethod as claimed in claim 2, wherein said method is a method forproducing an unsaturated aldehyde and an unsaturated carboxylic acidthrough gas-phase catalytic oxidation of isobutylene with molecularoxygen.
 8. The method as claimed in claim 2, wherein said method is amethod for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid through gas-phase catalytic oxidation of tertiarybutanol with molecular oxygen.
 9. The method as claimed in claim 1,wherein said catalyst is represented by the following formula (I):Mo_(a)Bi_(b)Fe_(c)M_(d)X_(e)Y_(f)Z_(g)Si_(h)O_(i)  (I) wherein Mrepresents at least one element selected from the group consisting ofcobalt and nickel, X represents at least one element selected from thegroup consisting of chromium, lead, manganese, calcium, magnesium,niobium, silver, barium, tin, tantalum and zinc, Y represents at leastone element selected from the group consisting of phosphorus, boron,sulfur, selenium, tellurium, cerium, tungsten, antimony, and titanium, Zrepresents at least one element selected from the group consisting oflithium, sodium, potassium, rubidium, cesium, and thallium, a is 12, bis from 0.01 to 3, c is from 0.01 to 5, d is from 1 to 12, e is from 0to 8, f is from 0 to 5, g is from 0.001 to 2, h is from 0 to 20, and iis the atomic ratio of oxygen that fulfills the requirement of thevalence of each component.
 10. The method as claimed in claim 9,comprising controlling reaction pressure and the molar ratio of oxygento the raw material in such a way that a rate of reaction of the rawmaterial is kept constant in the temperature range of from (TA−15)° C.to TA° C.
 11. The method as claimed in claim 9, wherein said method is amethod for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid through gas-phase catalytic oxidation of propylene withmolecular oxygen.
 12. The method as claimed in claim 9, wherein saidmethod is a method for producing an unsaturated aldehyde and anunsaturated carboxylic acid through gas-phase catalytic oxidation ofisobutylene with molecular oxygen.
 13. The method as claimed in claim 9,wherein said method is a method for producing an unsaturated aldehydeand an unsaturated carboxylic acid through gas-phase catalytic oxidationof tertiary butanol with molecular oxygen.
 14. The method as claimed inclaim 1, wherein the reaction pressure at the start of the reaction is95 to 105 kPa and is 110 to 120 kPa at the end of the reaction.
 15. Themethod as claimed in claim 1, wherein the reaction pressure risescontinuously with the progress of the reaction of the raw material. 16.The method as claimed in claim 1, wherein the reaction pressure risesstepwise with the progress of the reaction of the raw material.
 17. Themethod as claimed in claim 16, wherein the reaction pressure rises intwo steps or more.
 18. The method as claimed in claim 17, wherein thereaction pressure rises in two steps, wherein a first reaction pressureis set at 95 to 105 kPa, a middle reaction pressure is set at 100 to 110kPa, and a final reaction pressure is set at 110 to 120 kPa.